I did make changes to the components, namely, the Accelero Extreme III on the
Zotac GTX 970 and the Noctual DH-D9L with two in-line fans. By this time, the
original system had been long pulled apart, so changing the components didn't
take any more effort.

The first change was to see if the reduced impedance of the bottom intake vent
would help VGA cooling. The Accelero Extreme III has three fans which draw directly
from the bottom vents. The absence of the radiator (which is part of the Hybrid
II) would help keep in/out airflow impedance to a minimum. And besides, the
Extreme III seemed a little easier to mount than the Hybrid II.

The CPU cooler change was made because I like the idea of CPU fans blowing
the heat out of the case, rather than a top-down style cooler which blows the
heat all around for case fans to then push out. With a second 92mm fan in push-pull
mode, I figured the two fin stacks would work most effectively.

Again, installing the Accelero Extreme III was mainly fussy, but not "hard".
Getting even pressure on the GPU was the essential task. Despite the inclusion
of many different height spacers, you need to pay close attention to ensure
even, tight pressure on the GPU.

Accelero Extreme II installation, viewed from top edge of VGA card.

Config 5 without dust filters, all components installed, with arrows showing
airflow. Top fan blows down on the Noctua CPU cooler, whose two fans get
also air from the open back panel vents & blow towards the front.
The retail Noctua NF-A9 PWM fan package includes a handy 4-pin Y-splitter
cable, used to keep both fans on the CPU fan header of the Gigabyte motherboard.
Accelero Extreme III fans pull air from bottom vent and blow up. Front
fans blow out: When gaming, the area in front of the PC does get warm.
Note small piece of black colored close-cell foam positioned between the
second and third VGA fan. This was stuck in place with a couple drops
of super glue. It heps to keep the VGA card from drooping on that side
with the weight, reducing the pressure on the PCIe slot. If you do something
similar, make sure no fan blades get stopped.

The front portion of the top vents were blocked off with a piece of heavy
paper. This is to keep airflow in control. Ideally, the front fans should
not pull air in from those top vents, which would be an airflow short
circuit that bypasses the CPU heatsink.

Control of the Arctic VGA cooler was an issue. I'd been using the ASUS GPU
Tweak utility for GPU fan control before, but the lowest speed that would
allow is 35%. With the fans on the Arctic cooler, 35% is very smooth and broadband,
but far too loud, in the mid-20s [email protected] The small 4-pin plug on the Arctic
cooler has four conductors for its fans, like the original Zotac cooler, but
for some reason, none of the montoring software picked up the RPM.

Since GPU Tweak could not get me to a lower speed, I uninstalled it and tried
MSI RIVA Tuner. It got to the Arctic cooler to 28% fan speed but this
was still far too noisy.

Stymied, I resorted to the 4-pin Molex to 7V/12V adapter Arctic supplies with
its VGA coolers. This connects the cooler fans directly to the PSU for either
12V or 7V operation. It's a pretty basic fan control in this age of uber-sophisticated
software utilities. I didn't even try the 12V plug, going straight to 7V.

This was the right setting. I could tell the SPL was no higher than 20 [email protected],
and it was a smooth sound, far better than any of the earlier iterations of
this build. Those filters definitely exact an acoustic price.

After playing around with the Advanced Smart Fan section in Gigabyte's System
Information Utility while keeping the system under high load (Furmark + Prime95x2),
I settled on a couple of relatively simple custom profiles for the CPU fan and
the three case fans.

Custom CPU fan profile.

Custom profiles were similar for all three case fans.

With these settings, after half an hour of Furmark + Prime 95x2, the CPU was
stable at 70°C, the GPU at 83°C. The latter was much higher than with
the Accelero Hybrid II-120, but the noise was far lower. All the other temperatures
reported by system sensors showed nothing amiss. The measured SPL was 19 [email protected]
at this point. A close look and listen confirmed that the last fan in the system,
the one in the Seasonic G550 power supply, might be spinning slightly faster
than at idle, but at a low enough level that its acoustic contribution was moot.

Thinking through the system details, I wondered again if the bottom feet gave
enough clearance for good unimpeded airflow to the VGA fans. You may recall
I turned the system on its side so the bottom intakes were facing left in an
earlier iteration, and with the dust filter in place, almost nothing changed.
This time, instead of putting the system on its side, I propped up the front
with a small block of wood, adding a little more clearance between intake vent
and the desktop. The effect, this time, was almost immediate, with GPU temperature
starting to drop the moment this was done. Five minutes later, the GPU temperature
had dropped 7°C, and this also helped the CPU, which dropped 3°C. All
this is summarized in the following images and tables.

Filterless Air 240 system propped up on a block of wood for a bit more
bottom intake clearance.

There's barely any difference in measured or perceived noise between idle
and full load.

AUDIO RECORDING

This recording was made with a high resolution, lab quality, digital recording
system inside SPCR's own 11 dBA ambient anechoic chamber, then converted to
LAME 128kbps encoded MP3s. We've listened long and hard to ensure there is no
audible degradation from the original 24/88 WAV files to these MP3s. They represent
a quick snapshot of what we heard during the review.

The recording starts with 7 seconds of ambient noise, then ~10 second segments
of the system at various states. For the most realistic
results, set the volume so that the starting ambient level is just barely audible,
then don't change the volume setting again while listening.